1. Field of the Invention
The present invention relates to an elevator speed controller which moves up and down a car via a rope wound around a sheave by driving this sheave by a motor.
2. Description of the Related Art
FIG. 7 is a schematic block diagram of an elevator which is called a well bucket type out of rope type elevators. In FIG. 7, a motor 4 is installed on the roof of a building and rotates a sheave 11 which is part of an elevator mechanical system 10. A rope 12 is wound around the sheave 11. A car 13 is connected to one end of the rope 12 and a counter weight 14 is connected to the other end of the rope 12. This counter weight is set at the mass almost equal to the car 13 to balance with it. So, when the car 13 is moved up or down by driving the motor 4, the counter weight 14 serves to reduce load of the motor 4, save energy and downsize the motor.
FIG. 8 is a block diagram showing the structure of the speed control system of the elevator mechanical system shown in FIG. 7. In FIG. 8, 1 is a car speed command value setting means to set a car speed command value upon receipt of an elevator starting command and a known car speed command value that is set is added to a speed conversion means 2. The speed conversion means 2 converts a car speed command value into a speed command value of the motor 4 and adds a converted speed command value to a motor controller 3. The motor controller 3 controls the current of the motor so that a speed detected value by a motor speed detecting means 5 follows a speed command value converted by the speed converting means 2. So, a car speed is controlled so as to become equal to a car speed command value.
The conventional elevator speed controller described above controls the speed of the car 13 by driving the motor 4 according to a desired car speed command value regarding the elevator mechanical system 10 to be a rigid body. At the time, vibrations of a car caused by jumping of passengers, distortion of rails, resonance of the mechanical system, etc. were suppressed mechanically by installing dampers, vibration isolating rubbers and the like.
However, since an elevator is a system of which natural frequency changes largely due to load and the position of a car, it couldn't suppress oscillation to substantially zero by such a mechanical vibration isolating means as dampers, vibration isolating rubbers, etc. and vibrations generated at some specific floor or specific load became a problem. This tendency was remarkable in case of a long distance and super high-speed elevator of which a change of natural frequency was specifically large.
Further, in order to realize the high accurate speed control it is desirable to always update a control gain according to these detected values irrespective of change in load and a car position; however, as there is no guide line and an enormous adjusting time is required in the trial and error, a control gain was so far set at a constant level. However, it became necessary to readjust the control gain some time according to specifications and demanded performance of an elevator and as the adjustment was made in the trial and error, its efficiency was also low.